i've had achari chicken at raaga in falls church. i do not know if it is "authentic" per se. you can call ahead and talk to the chef (i think his name is ramesh), and he will make any dish you want.

i know he did that for someone wanting a good, hot punjabi curry. i know he has made us special dishes (mine with shrimp) when we ask. he has told us to give him one day's notice and he can get anything (like when we mentioned doing a special fish, for example).

Even if you did find it, I know most chefs in Indian restaurants use ready pickles to give it that achari flavour, which is of course not the authentic way. The idea of the dish is to use pickling spices as the dominant spice mix to impart a pickle-like flavour to your dish, which typically must include nigella seeds, fenugreek seeds, mustard seeds and chironji (cuddapah almond)